function P = comp_dof_strain(H)
% function P = comp_dof_strain(H)
% The function is similar to matrix-modification-method
% the c^1-constrain condition is elliminated by d.o.f. dense
% the element-by-element assemble procedure can also
% archive this goal.
%

%
% The foundamental idear is to find the "-1" in smoothness matrix
% which is the constrained d.o.f, be careful to cancel the redundance.
% This idear is a little bit like the MDS game of P. Alfeld.
% The last modification matrix is P, whos row represent the
%